1. Field of the Invention
This invention relates to the field of silver recovery from silver-containing waste fluids and more specifically, this invention relates to an apparatus with improved flow-through characteristics for achieving this recovery. Still more specifically, this invention relates to an improved apparatus which can be used for recovering silver from spent, photographic fluids such as fixers and developers, one which has a longer service life during use and can recover more silver per unit of use.
2. Description of the Prior Art
There are a host of prior art references which relate to elements useful in recovering silver from spent, waste, silver-containing fluids such as photographic processing fluids. Many of these references describe devices which employ base metals higher in the electromotive series than silver (herein called "media") in order to effect an exchange of silver for some less expensive metal. These prior art devices usually employ some kind of container to contain this media and pass the waste fluids through this container in order to effect this exchange. Improvements to the process are known. In assignee's patent to Williams, U.S. Pat. No. 4,740,244, Apr. 26, 1988, which is incorporated herein by reference, there is described such as improvement. In this case, steel wool as the media, improvement is noted by the addition of small amounts of a copper or cadmium salt present, to this exchange media. In a divisional application of the aforesaid Williams, now issued as U.S. Pat. No. 4,854,552, Aug. 8, 1989, also incorporated by reference, an apparatus for precious metal recovery from these waste, processing fluids, is also described. Graham et al., USSN No. 07/367,394, filed June 16, 1989, the essence of which is also incorporated herein by reference, describes a particularly useful apparatus which is durable and leak proof. These and other prior art references all describe the use of a filler element such as finely divided iron as the exchange media.
Most of these prior art references employ essentially the same apparatus design for containing the exchange media. These designs are usually a container made from some impervious material such as a plastic. The exchange media is placed within this container which also has an inlet and an outlet for the passage of the waste fluid therein. Some of the prior art elements are sealed while others can be opened for re-use and thus this latter device usually has some kind of top. The aforementioned Graham et al. application describes an improved, re-usable device which is tight and leak proof compared to that described elsewhere in the prior art. All of these prior art elements are usually employed to recover silver from waste, photographic processing fluids such as fixers and developers. In this use, they are usually attached to end of processor used to develop and process the photographic films. It is sometimes conventional to use more than one of these devices to insure complete recovery of the precious, silver metal and to insure that essentially no silver is discarded to the drain or sewer lines. Sometimes, the waste processing fluids contains other matter which tends to plug the recovery system. Thus, most of the prior art also have some sort of relief or by-pass device associated therewith in case plugging occurs. Another problem that occurs is leakage. Since the photographic fluids are corrosive, gaskets used to seal the system can be corroded and leaking can occur. Still another problem is space. The industry that uses these automatic film processors usually put these processors in small darkrooms. When it is necessary to use more than one of these recovery devices, there is a crowding problem since most of the prior art elements cannot be stacked conveniently. Plugging in the conventional, prior art canister systems usually occurs when these systems are left standing when the processors to which they are connected are idle, for example. At this point, fluid left in the canister is at a level near the conventional stand-pipe and deposits are formed therein. When the system is then activated, these deposits impede fluid flow. Most of these problems are solved by the aforementioned Graham et al. application. However, it is also desirable to have a recovery unit with high flow-through characteristics and thus improved time of use. It is also desirable to simplify the construction and manufacture of this units. None of the prior art elements can fully achieve these desired characteristics.